Either way, here are two excellent FREE resources for you:
Noteflight - If you've ever wanted to write some music but never quite been able to hear what it sounds like, Noteflight is the site for you. Not only can you write for different instruments, but it will play back what you've written. It does require email registration, so be sure to talk with your parent/guardian first.
Printable Staff Paper - If you want to avoid the hassle of registering online and just want some staff paper to jot something down, this site is for you!